Millions of patients worldwide suffer from hip, knee, and ankle joint disorders, including quadriceps weakness, Patellofemoral Pain Syndrome, or from injuries, stroke, post-polio, multiples sclerosis, or SCI. An improvement in lower extremity assistive devices will benefit some or all of these patients. However, with few exceptions, orthotic options for this population are limited to passive technologies that cannot provide assistance necessary to replicate the function of an unaffected limb. Accordingly, there is great potential for the development of electromechanical devices to drastically increase the quality of life of this population. Gait pathologies and musculoskeletal disorders are often stabilized using a leg orthosis, typically consisting of a crude hard piece of material formed to the wearer's leg. Recently, new orthotic technologies have been introduced that rigidly lock the knee in the stance phase and unlock it in the swing phase of the gait. The rigid support of the knee in the stance phase of the gait results in low gait speed, joint pain due to the absence of shock absorption mechanisms and a pathological gait. The rigid assistance of the ankle highly hinders propulsion and reduces the gait speed.
To overcome these problems, new orthotic technologies require incorporation of compliance tuned based on the gait and subject conditions. Thus, there is a need in the art for a quasi-passive friction-based impedance modulation device for orthotic applications. The present invention satisfies this need.